The Flanchford Road site in Reigate, Surrey was purchased by Stanton Construction whose development proposal entailed the refurbishment of three existing cottages and the construction of three new residential properties.

The site was previously utilised as a petrol filling station and vehicle repair workshop and site investigation identified groundwater contamination at concentrations that posed a risk to the underlying aquifer and nearby SSSI. It was at this stage that Ash Remediation Management became involved with the project and their first task was to prepare and gain Local Authority approval of a remediation strategy.

The remediation strategy was promptly agreed and the scope of the remedial work is summarised below:

• Empty, clean and decommission the three underground storage tanks.
• Excavate and recycle any grossly contaminated soils contained within the tank void.
• Carry out chemical oxidation treatment of the contaminated groundwater plume.
• Monitor groundwater quality for six months.

In addition to the remedial work Ash Remediation Management also carried out the controlled demolition of the vehicle repair garage. All demolition material was carefully segregated before been sent for recycling.

The project ran smoothly from start to finish and the on site stage of work was completed in a little under three weeks. Ash Remediation Management compiled a Verification Report summarising the work completed which enabled release of the related planning conditions.

Client – Homes and Community Agency

Principal Contractor – Lumsden and Carroll

Consulting Engineer – Halcrow

Location – Stockton-on-Tees

Contract Value – £400K

The North Shore project is located on the north bank of the River Tees adjacent to the Infinity Footbridge in Stockton-on-Tees. Diesel oil based contamination had been detected in the River Tees and investigation identified the source as a number of underground fuel tanks. The diesel was migrating through the groundwater and Ash Remediation Management installed a groundwater treatment barrier to sever the pollution linkage pathway.

Each barrier system installed by Ash Remediation Management is bespoke and numerous design parameters are taken into account prior to installation. Variables considered include its position and depth in relation to the contaminant source, treatment capabilities and design life. These important design decisions are augmented with groundwater modelling and column testing. Prior to the installation of the North Shore barrier, the final design was agreed with the consulting engineer and Environment Agency.

The resulting design was applied using the soil mixing capabilities of a piling rig. The treatment slurry was produced in an automated batching plant and delivered to the rig via a semi automated pumping system. As the auger rotated slurry was injected through the modified drilling head and mixed with the surrounding media. During the mixing process the rig’s on board computer generated real time drilling data which enabled the driver to ensure equal dispersion and homogenisation of the slurry. Drilling data was recorded daily and used in the quality control process.

On completion of installation the regulator approved monitoring scheme commenced. Monitoring wells upstream and downstream of the barrier were sampled for a period of two years. Upstream wells provided data on water quality impacting upon the barrier and those installed downstream illustrated the quality of water migrating through.

The monitoring demonstrated the success of the barrier system and the associated report produced by Ash Remediation Management was approved the Environment Agency.

The project was completed on time, on budget with a zero accident record.

Client – Homes and Community Agency

Principal Contractor – Carillion Civil Engineering

Consulting Engineer – AECOM

Location – Lambton

Contract Value – £400K

The Lambton site historically operated as a colliery, cokeworks, firebrick works as well as a gas storage and purification facility. Located in Tyne and Wear, the site covers an approximate area of 65 hectares.

Ammonium was identified in groundwater at concentrations requiring remedial action. Commissioned by Carillion PLC (on behalf of a regional development agency), Ash Remediation Management addressed this issue through the installation of an in-situ water treatment barrier. The objective of the system was to mitigate the risk of ongoing migration of ammonium contaminated water to a nearby watercourse ( The Herrington Bern) by severing the pollution linkage pathway.

Ash Remediation Management acquired Environment Agency approval of the remedial scheme and the installation commenced in June 2009. The six week programme entailed the installation of relatively impermeable (270m) and relatively permeable sections (200m) of barrier and was completed 2 weeks ahead of schedule and within budget.

The barrier system was installed using a piling rig equipped with a soil mixing drill head, which is designed to reduce the amount of spoil produced. As the drilling head progresses the treatment slurry is injected via ports located within. Once the desired drilling depth has been achieved the withdrawal process of continued auger rotation further facilitating homogenisation of the soil mixed column commences. A high level of quality control was acvhieved by maximising the use of the rigs on board computer which measured numerous drilling parameters.

In order to assess the efficacy of the barrier system, a long term monitoring regime was drawn up and submitted to the Environment Agency. With the ultimate objective to monitor the quality of water migrating through the barrier, 4 No. wells were installed downstream of the relatively permeable barrier sections. Additionally, 3 No. wells were installed upstream in close proximity to the relatively permeable sections to illustrate the quality of water impacting upon the barrier. Two further wells were installed upstream at distance from the system to provide some data on background water quality. The monitoring period has now ended and the final laboratory results have proved the system has been a success.